The computer industry uses integrated circuit dies contained in microelectronic packages and connected to other components of a computer system. In order to function properly a die must be physically, electrically, and thermally connected to its packaging, and a microelectronic package must be similarly connected to a motherboard or another system component. Such connections are frequently accomplished using a metallic bonding solution employing lead-free solder based on tin, indium, or a similar material. Conventional soldering techniques involve melting and therefore require high-temperature excursions, the magnitude of which depend on the melting point of the solder. These high temperature excursions lead to high levels of thermal stress in the solder interconnect joints, and this in turn often results in an interconnect joint that is weak, has low stiffness, tends to crack, and has other reliability problems. The high temperatures also are incompatible with a wide variety of materials whose use would be desirable in microelectronics technology. Moreover, solder-based interconnect joints are relatively expensive due to the expense of the solder material.
Low-melting point solders, such as tin-bismuth, do exist, but interconnect joints formed from these materials suffer from their own reliability issues that significantly limit their usefulness. Accordingly there exists a need for an interconnect joint that may be formed at temperatures significantly lower than temperatures required by existing technologies, thus lowering the stresses experienced by the package (and thereby reducing the occurrence of many stress-related package failures), enabling the use of a variety of low-temperature materials, and providing a larger process window for other package materials.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.